Projection type image display apparatus with light masking

ABSTRACT

According to the present invention, a projection type image display apparatus enables control of a large amount of light masking through a light-masking unit while maintaining a uniform illumination distribution in an area to be illuminated by the illumination light. The apparatus uses two array lenses on which lens cells are arranged in matrix form, where light-masking unit masks the array lens installed on the light source side in their particular area. The light-masking unit adjusts the amount of light emitted from the light source. The light-masking area of lens cells adjacent to lens cells closest to an optical axis is made smaller than the light-masking area of other cells.

CLAIM OF PRIORITY

The present application is a Continuation of U.S. application Ser. No.15/173,253, filed on Jun. 3, 2016, which is a Continuation Applicationof U.S. application Ser. No. 14/258,385, filed Apr. 22, 2014, now U.S.Pat. No. 9,383,634, which is a Continuation of U.S. application Ser. No.13/867,425, filed on Apr. 22, 2013 now U.S. Pat. No. 8,727,542, which isa Continuation of U.S. application Ser. No. 13/361,588, filed on Jan.30, 2012, now U.S. Pat. No. 8,425,054, which is a Continuation of U.S.application Ser. No. 13/209,153, filed on Aug. 12, 2011, now U.S. Pat.No. 8,142,025, which is a Continuation of U.S. application Ser. No.12/813,994, filed on Jun. 11, 2010, now U.S. Pat. No. 8,020,998, whichis a Continuation of U.S. application Ser. No. 11/500,969, filed on Aug.9, 2006, now U.S. Pat. No. 7,753,535, which claims priority fromJapanese application serial no. JP 2005-230230, filed on Aug, 9, 2005,the entire contents of each of which are hereby incorporated byreference-application.

BACKGROUND OF THE INVENTION

The present invention relates to a projection type image displayapparatus which forms an optical image based on a picture signal bymeans of an image display element and projects the optical image on ascreen or the like.

With a conventional projector optical system, when optical modulation ofthe image display element is performed in order to minimize theluminance, a phenomenon called “grayish black” occurs with which thelight absorbed by a light-exiting polarization plate is not sufficientand the screen luminance does not decrease. The light-exitingpolarization plate aligns the polarization of light beams modulated bythe image display element.

For this reason, there is a means for improving the contrast by reducingthe minimum luminance of a projection type image display apparatusthrough light control means for changing the light volume of the entirescreen based on external signals, other than a light valve. Externalsignals in this case include a picture signal, an external environmentmeasurement signal, a signal intentionally manipulated by user, etc. Asone example of the above means, techniques using a light-masking unitfor changing the amount of masking light according to an image signal inan illumination optical system are disclosed in U.S. Patent ApplicationPublication No. US 2003/0086265A1, Japanese Patent Laid-open No.2005-17500 and Japanese Patent Laid-open No. 2005-31103.

SUMMARY OF THE INVENTION

To widen the dynamic range of a projection type image display apparatus,it is necessary to increase the amount of light masking by alight-masking unit arranged in an illumination optical system. Toincrease the amount of light masking by the light-masking unit, it isnecessary to increase the light-masking section with which light-maskingplates included in the light-masking unit mask light beams.

However, there has been a problem that, with the increase in the amountof light masking, the illumination distribution in an area to beilluminated by illumination light is likely to become nonuniform becauseof a decrease in the number of second light source images superimposedon an area to be illuminated by an illumination optical system formed byarray lenses. There has been another problem that, when thelight-masking unit turns or moves a light mask to perform light masking,the variation of the illumination distribution when the light mask ismoved or turned is likely to be reflected on a screen.

In particular, the image display element, like a liquid crystal displayelement, has such a characteristic that degrades more the contrastperformance with increasing angle of the incident light with respect tothe normal line of the element surface. The above-mentioned problemsstand out, if light masking is performed starting from pieces of lighthaving a larger angle with respect to the normal line of an imagedisplay element, which adversely affects the contrast performance of theimage display element, in order to improve the contrast performance ofthe projection type image display apparatus.

An object of the present invention is to enable control of a largeamount of light masking through a light-masking unit while maintaining auniform illumination distribution in an area to be illuminated by theillumination light.

Another object of the present invention is to provide a projection typedisplay apparatus having a wide dynamic range, excellent power of imageexpression, and the ability to respond the environment and usersintention.

According to an aspect of the present invention, with a projection typeimage display apparatus which makes uniform the light of the lightsource using two array lenses on which lens cells are arranged in matrixform, light-masking unit masks the array lens installed on the lightsource side in their particular area. The light-masking unit adjusts theamount of light emitted from the light source. The light-masking area oflens cells adjacent to lens cells closest to an optical axis is madesmaller than the light-masking area of other cells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram showing a configuration of an array lens on thelight source side.

FIG. 1B is a diagram showing an example of superimposition oflight-masked cells.

FIG. 1C is a diagram showing another example of superimposition oflight-masked cells.

FIG. 2 is a graph showing the illumination intensity of penetratinglight beams at the array lens surface on the light source side withrespect to the distance along the direction from an optical axis,recognizing a point intersecting with the optical axis as origin.

FIG. 3 is a diagram showing the distribution of outgoing light emittedfrom the light source.

FIG. 4 is a diagram showing an example of rate of contribution to theillumination intensity of each cell of the array lens.

FIG. 5 is a diagram showing an example of arrangement and light-maskingsection of the array lens.

FIG. 6 is a diagram showing a configuration of an optical system.

FIGS. 7A-7D are diagrams showing examples of arrangement of alight-masking unit.

FIGS. 8A-8C are diagrams showing examples of a method of moving a lightmask of the array lens.

FIGS. 9A-9B are diagrams showing another example of light-maskingsection of the array lens.

FIGS. 10A-10C are diagrams showing configurations of the array lens.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An embodiment of the present invention will be explained below withreference to the accompanying drawings. In each drawing, the samesymbols are assigned to elements having a common function and duplicatedexplanations are omitted. For components which should be discriminatedfor each colors light path, subscript R, G, or B is supplied to areference numeral. The subscript is omitted unless the omission causesinconvenience in explanation. Subscript a, b, c, or d supplied to areference numeral indicates a component indicated by the referencenumeral or the optical axis or optical direction regarding a componentindicated by the reference numeral.

First, an embodiment of the present invention will be explained belowwith reference to FIG. 1 to FIG. 5.

A projection type image display apparatus in an embodiment of thepresent invention includes a light source, two array lenses sequentiallyarranged from the near side of the light source along the optical axisof the light emitted from the light source, a uniform illumination unitwhich makes uniform the illumination distribution of the light inputtedfrom the light source, and a light control unit which adjusts the amountof light emitted from the light source. The uniform illumination unitincludes a superimposing lens which superimposes on the illuminationsurface a plurality of second light source images formed by the twoarray lenses. The light control unit is installed on the optical axis ofthe light emitted from the light source. Furthermore, the amount oflight emitted from the uniform illumination unit can be adjusted bycontrolling the light control unit based on information from external.Of the two array lenses, at least one installed on the light source sideincludes a plurality of substantially rectangular lenses inpredetermined array arrangement. The light control unit is installed onthe incidence side of two array lenses, between the two array lenses,between the two array lenses and the superimposition lens, or on thelight-exiting side of the superimposition lens. The light control unitis a light-masking unit which adjusts the light volume of theillumination light. In operation, the light control unit masksillumination light beams inside the uniform illumination unit or beforeand after the uniform illumination unit by moving or turning one or morelight-masking plates in a predetermined direction. When thelight-masking unit adjusts the amount of light emitted from the lightsource to the minimum level, the shape of the light-masking plates issuch that the area of a predetermined cell is smaller than the area ofother cells when the light-masking plates are projected on each cell ofthe array lens on the light source side.

An object of light masking only for a predetermined area of apredetermined cell is to keep more uniform the illumination distributionin the area to be illuminated by the illumination light while increasingthe amount of light masking by the light-masking unit. Light maskingonly for a predetermined area of a predetermined cell is specificallyexplained below.

An integrator optical system using an array lens obtains more uniformillumination distribution generally by superimposing second light sourceimages of the illumination distribution of each cell on the area to beilluminated. The rate of contribution to the illumination intensity forsuperimposed illumination distribution depends on each array lens cell.When the light-masking plates partially mask light beams which penetratethrough each cell, the illumination distribution of each cell becomesnonuniform because of nonuniform light masking by the light-maskingplates. Therefore, since the illumination distribution of cells havingthe highest rate of contribution to the illumination intensity has alarge effect on the illumination distribution superimposed on an imagedisplay element, the illumination distribution superimposed on the imagedisplay element becomes most nonuniform when this cell is partiallylight-masked. As increasing number of cells are light-masked by thelight-masking plates and accordingly decreasing number of cells are notsubject to masking of light beams, the illumination distribution ofcells having a high rate of contribution to the illumination intensityhas a larger effect on the illumination distribution superimposed on theimage display element, thereby increasing the ununiformity of theillumination distribution superimposed on the image display element whenthis cell is partially light-masked.

When the light-masking unit thus adjusts the amount of light emittedfrom the light source toward the decreasing direction, light masking isperformed so that the area of the light-masking section at cells havinga high rate of contribution to the illumination intensity is smallerthan the area of the light-masking section at other cells. Thisconfiguration makes it possible to obtain larger amount of light maskingwhile maintaining more uniform illumination distribution superimposed onthe image display element.

In the process where the light-masking unit adjusts the light volumetoward the minimum level, if light beams of many cells remain notlight-masked, even light beams penetrating through cells having thehighest rate of contribution to the illumination intensity have acomparatively small effect on the ununiformity of the illuminationdistribution. In this condition, there is a small effect on theununiformity of the illumination distribution superimposed on the imagedisplay element even if cells having a high rate of contribution to theillumination intensity are partially or entirely light-masked. However,after cells having a high rate of contribution to the illuminationintensity are entirely light-masked, the ununiformity of theillumination distribution is most affected when cells without entiremasking of light beams, having the highest rate of contribution to theillumination intensity, are partially light-masked. Therefore, when thelight-masking unit adjusts the amount of light emitted from the lightsource to the minimum level, light-masking control is performed so thatthe area of the light-masking section at cells other than ones withentire masking of light beams or ones with partial transmission of lightbeams, having the highest rate of contribution to the illuminationintensity, is smaller than the area of the light-masking section atother cells. This configuration makes it possible to obtain largeramount of light masking while maintaining more uniform illuminationdistribution superimposed on the image display element.

Furthermore, in order to increase the amount of light masking, whencells with partial transmission of light beams, having the highest rateof contribution to the illumination intensity, are partiallylight-masked, it is desirable that the area of the light-masking sectionat the cells be not more than one half of area of the cells. The reasonis explained below with reference to FIG. 1.

In FIG. 1A, an array lens is viewed from the optical axis direction. Onthe array lens, rectangular cells are arranged in directions which arein parallel with two arbitrary axes perpendicularly intersecting in aplane of the array lens. Reference numeral 401 denotes an edge line of acell; 402, one axis of the two axes; and 403, the other axis of the twoaxes. With the array lens configuration shown in FIG. 1A, there arepaired cells which are arranged symmetrically to the optical axis, suchas hatched cells 404 and 405 in FIG. 1A.

These cells 404 and 405 are paired cells. If the area of thelight-masking section at paired cells is not more than one half of thearea of each cell, the illumination distribution for one cell can beformed by overlapping light-transmitting sections of the paired cellsby, for example, a light-masking method shown in FIG. 1B. With pairedcells 404 and 405 in FIG. 1B, light-transmitting sections are 404 a and405 a, and light-masking sections are 404 b and 405 b. If the area oflight-masking sections 404 b and 405 b is not more than one half of thearea of one cell, in other words, if the area of light-transmittingsections (opening sections) is not less than one half of the area of onecell, illumination distribution 406 after superimposition has no sectionwith little illumination intensity, resulting in uniform illuminationdistribution.

On the other hand, if the area of light-masking sections of paired cellsis not less than one half of the area of each cell, in other words, ifthe area of light-transmitting sections (opening sections) is not morethan one half of the area of each cell, illumination distribution forone cell cannot be formed even by overlapping light-transmittingsections of paired cells as shown in FIG. 1C. As a result, a portionwith extremely low illumination intensity occurs. With paired cells 404and 405 in FIG. 1C, light-transmitting sections are 404 c and 405 c, andlight-masking sections are 404 d and 405 d. If the area of light-maskingsections 404 d and 405 d is not less than one half of the area of onecell, illumination distribution 406 after superimposition has sections406 c with high illumination intensity and a section 406 d withextremely low illumination intensity, resulting in remarkably nonuniformillumination distribution. With paired cells having a low rate ofcontribution to the illumination intensity, there is a small effect onthe illumination distribution after superimposition of light beams ofeach cell. With paired cells having a high rate of contribution to theillumination intensity, however, there is a large effect on theillumination distribution, resulting in nonuniform illuminationdistribution on the image display element on which illuminationdistribution of all cells is superimposed. Therefore, it is desirablethat the area of the light-masking section at cells having the highestrate of contribution to the illumination intensity or cells other thanones with entire masking of light beams, having the highest rate ofcontribution to the illumination intensity, be not more than one half ofthe area of the cell.

Generally, cells for an array lens are arranged in a plane which isperpendicular to the optical axis of the light source, symmetrically tothe optical axis. Therefore, taking into account that the illuminationdistribution of each cell is superimposed on the image display element,it is desirable that the light-masking section by light masks includedin the light-masking unit be realized symmetrically to the optical axisin order to prevent the deviation of the illumination distribution. Witha configuration having an array lens shown in FIG. 1A, for example, itis desirable that light masking be performed particularly in linesymmetry to the two axes, i.e., in point symmetry to the center of thearray lens through which the optical axis penetrates in order to preventthe deviation of the illumination distribution.

FIG. 2 shows a graph with the vertical axis assigned the illuminationintensity 411 of light beams at the array lens surface on the lightsource side and the horizontal axis assigned the distance along thedirection from the optical axis to outside, recognizing a pointintersecting with the optical axis as origin. As shown in FIG. 2, a peakof the illumination intensity exists not near the optical axis but atpositions slightly apart from the optical axis. The reason is explainedbelow with reference to FIG. 3.

FIG. 3 indicates a light source 1, a reflecting surface 2000 of areflecting mirror, and distribution 412 of the light emitted from thelight source. For convenience of explanation, the distribution 412 ofthe emitted light is represented on the premise that no reflectionoccurs on the reflecting surface 2000 of the reflecting mirror. As shownin FIG. 3, the amount of light emitted in the optical axis direction 414is smaller than the amount of light 413 emitted in a direction at anangle with the optical axis direction. Therefore, when light beamshaving the illumination distribution reflect off the reflecting surface2000 of the reflecting mirror and then advance in parallel with theoptical axis direction, the illumination distribution as shown in FIG. 2is obtained.

FIG. 4 indicates the rate of contribution to the illumination intensitywhen the amount of light emitted from the light source is adjusted tothe maximum level. In FIG. 4, a numeral in each cell indicates the rateof contribution to the illumination intensity of the cell on the imagedisplay element 18 (in FIG. 6) when the amount of light emitted from thelight source is adjusted to the maximum level. Cells having the highestrate of contribution to the illumination intensity are included in cellsections 422 adjacent to a cell section 421 at the center of the arraylens 3 through which the optical axis penetrates. The calculation of therate of contribution to the illumination intensity can be simulatedusing, for example, illumination optical system evaluation and designsoftware “ODIS” from Yoshida Optical Laboratory of Japan or opticaldesign and evaluation program “CODE V” from ORA (Optical ResearchAssociates) of the U.S.A. The simulation procedure includes theevaluation of the total amount of light beams A for all cells used,light masking (setting the transmission factor to 0%) or narrowing downof the aperture except for one cell, and measurement of the amount oflight beams B for that one cell. The rate of contribution to theillumination intensity is represented by B/A×100. This process isperformed for each cell of the array lens. Based on the illuminationdistribution characteristic shown in FIG. 3, cells having the highestrate of contribution to the illumination intensity in FIG. 4 are onesincluded in the cell sections 422 adjacent to the center cells but notones included in the center cell section 421.

Therefore, by performing light masking so that the area of thelight-masking section at cells adjacent to the center cells may besmaller than the area of the light-masking section at other cells,larger amount of light masking can be obtained while maintaining uniformillumination distribution superimposed on the image display element.Furthermore, the rate of contribution to the illumination intensity atthe center cells is lower than that at cells adjacent to the centercells. Therefore, by controlling light masking so that the area of thelight-masking section at center cells may be larger than the area of thelight-masking section at cells adjacent to the center cells, largeramount of light masking can be obtained while maintaining uniformillumination distribution superimposed on the image display element.

The above-mentioned light-masking control is necessary particularly toperform light masking from the minimum amount of emitted light to about20% of the maximum amount of emitted light. The reason is explainedbelow.

Generally if the image display element, like a liquid crystal displayelement, has such a characteristic that degrades more the contrastperformance with increasing angle with respect to the normal line of theelement surface of the incident light, light masking is performed usinga light-masking unit starting from pieces of light having a larger anglewith respect to the normal line of an image display element whichadversely affects the contrast performance. Eventually, when thelight-masking unit is adjusted so that the amount of light emitted fromthe light source may be minimized, only some cells near the centertransmit light beams. In an example shown in FIG. 4, the sum of the rateof contribution to the illumination intensity of the sections 422 formedby four cells adjacent to the center cells, in line symmetry to the twoaxes, accounts for approximately 9 to 10% of the total value. When thelight-masking unit is adjusted so that the adjusted amount of emittedlight may be not more than 20% of the maximum amount of emitted light,the sum of the rate of contribution to the illumination intensity ofcells included in the sections 422 relatively becomes 40 to 50%.Therefore, when the sections 422 consisting of cells adjacent to thecenter cell section 421 are partially light-masked, there is a largeeffect on the ununiformity of the illumination intensity.

On the other hand, the rate of contribution to the illuminationintensity of other cells becomes not more than that at cells included inthe sections 422. Therefore, the effect on the ununiformity of theillumination intensity when cells other than ones adjacent to the centercells are partially light-masked is smaller than that when cellsadjacent to the center cells are partially light-masked. In particular,the rate of contribution to the illumination intensity at the centercells is 4 to 5% of the total amount of emitted light with the examplein FIG. 4. Therefore, even when the light-masking unit is adjusted sothat the adjusted amount of emitted light may be not more than 20% ofthe maximum amount of emitted light, the rate of contribution to theillumination intensity at the center cells is relatively about 25%.Therefore, the effect on the ununiformity of the illumination intensitywhen the center cells are partially light-masked is smaller than thatwhen cells adjacent to the center cells are partially light-masked.

Based on the above, it is effective that light masking is performed fromthe minimum amount of emitted light to about 20% of the maximum amountof emitted light and that the area of the light-masking section at cellsother than ones with entire masking of light beams, having the highestrate of contribution to the illumination intensity, or cells adjacent tothe center cells is smaller than the area of the light-masking sectionat other cells including the center cells.

When the light-masking unit adjusts the amount of light emitted from thelight source to the minimum level, the effect by the light-masking unitcan be made larger by making a condition that light beams penetratingthrough all cells are partially or entirely light-masked in each cell ofthe array lens on the light source side as shown in FIG. 5. FIG. 5shows, from the light source side, a condition that light masks 502 and503 of light-masking unit 501 is projected on a first array lens 3 (inFIG. 6). FIG. 5 shows a condition that the amount of light emitted fromthe light source is adjusted to the minimum level. A hatched section 425is a light-masking section and a section 426 is a light-transmittingsection. Of the light-masking section 425, section 504 is a sectionwhich is light-masked by a first light mask 502 and section 505 is asection which is light-masked by a second light mask 503.

In this case, cells having the highest rate of contribution to theillumination intensity, cells other than ones with entire masking oflight beams, having the highest rate of contribution to the illuminationintensity, or cells adjacent to the center cells are partiallylight-masked. Since the illumination distribution with partial lightmasking of these light beams has a large effect on the illuminationdistribution superimposed on the image display element, both theuniformity of the illumination distribution and the amount of lightmasking can be attained by making the area of the light-masking sectionat these cells smaller than the area of the light-masking section atother cells or center cells.

Referring to an example in FIG. 5, the light-masking section at cellshaving the highest rate of contribution to the illumination intensity,cells other than ones with entire masking of light beams, having thehighest rate of contribution to the illumination intensity, or cellsforming cell sections 422, adjacent to the center cell section or thecell section 421 contacting the optical axis is smaller than the area ofthe light-masking section at other cells. It should be noted that“adjacent to” means a cell and another adjacent to it share a side.

Therefore, when the amount of light masking is maximized, i.e., theamount of transmission light is minimized, a light-masking sectionformed by a first light mask 502 and a second light mask 503 has asection corresponding to each cell of the array lens 3 on the lightsource side. A cell and a corresponding section have such a positionalrelationship that they are specified by the same row and column when animage formed by projecting the light-masking surfaces projected on thelight source array lens is split in matrix form in the same manner ascells. Furthermore, the area (opening area) of the light-transmittingsection of a section corresponding to any one cell included in thesections 422 is lager than the area of the light-transmitting section ofa section corresponding to any one cell including the section 421. Forcells forming the cell sections 422, the area of the light-maskingsection is not more than one half of the area of these cells. Notlimited to the sections 421 and 422, the area of the light-transmittingsection in a section corresponding to each cell can be determined by therate of contribution to the illumination intensity. Specifically, it isdesirable that the area of the light-transmitting section be larger withhigher rate of contribution to the illumination intensity. With theexample in FIG. 4, therefore, since the rate of contribution to theillumination intensity decreases with increasing distance from thesections 422 to outside along the direction of an axis 402, it ispreferred that the area of the light-transmitting section be alsoreduced in incremental steps.

A configuration of a projection type image display apparatus isexplained below. FIG. 6 is a diagram showing a configuration of aprojection type image display apparatus. With the 3-plate projectiontype image display apparatus in FIG. 6, reference numeral 1 denotes alight source which is a white lamp such as an extra-high pressuremercury lamp, metal-halide lamp, xenon lamp, mercury xenon lamp, orhalogen lamp. The light source 1 is provided with at least onereflecting mirror 2 having a circular or polygonal light-exit opening.The light emitted from the light source 1 penetrates through lightvalves 14R, 14G, and 14B including an image display element, advancestoward a projection lens 200, and is projected on a screen 100. Thelight radiated from the lamp of the light source 1 is reflected, forexample, by the reflecting mirror 2 having a paraboloidal surface tobecome in parallel with the optical axis and then input into a firstarray lens 3.

A first array lens 3 splits the incoming light into a plurality of lightbeams with a plurality of lens cells arranged in matrix form and thenguides them so that they efficiently pass through a second array lens 4and a polarization conversion element 5. Specifically, the first arraylens 3 is designed so that the light source 1 and each lens cell of thesecond array lens 4 form a relationship of object and image (conjugate).Like the first array lens 3, the second array lens 4 having a pluralityof lens cells arranged in matrix form projects the shape of the lenscells of the first array lens 3 corresponding to each lens cell on animage display element 18 in the light valves 14. At this time, lightbeams from the second array lens 4 are aligned to a predeterminedpolarizing direction by the polarization conversion element 5.

Each projection image on each lens cell of the first array lens 3advances through a superimposing lens 6, a condenser lens 13, a firstrelay lens 15, a second relay lens 16, and a third relay lens 17 andthen is superimposed on the image display element 18 in the light valves14. The superimposing lens 6 is provided with an optical axis 300.

Since the first array lens 3 and image display element 18 are designedsuch that they form a relationship of object and image (conjugate), aplurality of light beams split by the first array lens 3 aresuperimposed by the second array lens 4 and a nearby superimposing lens6 and then projected on the image display element 18 in the light valves14, enabling illumination with highly uniform illumination distributionhaving a practically problem-free level.

In this process, when the light reflected by a reflecting mirror 7enters a dichroic mirror 11, for example, the B light (light in the bluecolor band) is reflected while the G light (light in the green colorband) and R light (light in the red color band) are transmitted by thedichroic mirror 11, resulting in color separation into two differentcolors. Then, the G+R light is separated into the G light and R light bya dichroic mirror 12. For example, the G light is reflected while the Rlight is transmitted by the dichroic mirror 12. Various types of colorseparation methods are assumed; for example, the dichroic mirror 11 mayreflect the R light and transmit the G light and B light, or it mayreflect the G light and transmit the R light and B light.

With the configuration in FIG. 6, the B light reflects off the dichroicmirror 11 and then a reflecting mirror 10, passes through a condenserlens 13B and then a light valve 14B for the B light, and enters alight-composition prism 21. The B light which penetrates through thecondenser lens 13B and enters the light valve 14B is referred to as LB.Of the G light and R light transmitted by the dichroic mirror 11, the Glight reflects off a dichroic mirror 12, passes through a condenser lens13G, enters and penetrates through a light valve 14G for the G light,and enters the light-composition prism 21. The G light which penetratesthrough the condenser lens 13G and enters the light valve 14G isreferred to as LG. The R light penetrates through the dichroic mirror12, condensed by the first relay lens 15, reflects off a reflectingmirror 8, further condensed by the second relay lens 16, reflects off areflecting mirror 9, further condensed by the third relay lens 17, andenters a light valve 14R for the R light. The R light penetrates throughthe light valve 14R and then enters a light-composition prism 21. The Rlight which penetrates through the relay lens 17 and enters the lightvalve 14R is referred to as LR.

The B light, G light, and R light which penetrated through respectiveimage display element 18 are combined by the light-composition prism 21to form a color image. This image passes through the projection lens200, such as a zoom lens, and then reaches the screen 100. An opticalimage formed on the image display element 18 in the light valves 14after light-intensity modulation according to an image signal (notshown) is projected on the screen 100 in magnified form through theprojection lens 200.

With an example in FIG. 6, the light-masking unit explained in FIG. 4and FIG. 5 is used as a light-masking unit 501. Although thelight-masking unit 501 in FIG. 6 is arranged between the first arraylens 3 and the second array lens 4 to mask light beams by turning thelight masks, they may be arranged between the light source 1 and thefirst array lens 3 as shown in FIG. 7A, between the second array lens 4and the polarizing conversion element 5 as shown in FIG. 7B, on thelight-exiting side of the polarizing conversion element 5 as shown inFIG. 7C, or on the light-exiting side of the superimposing lens 6 asshown in FIG. 7D. Therefore, when light-masking unit 501 is arrangedbetween the first array lens 3 and the light source 1, light beams afterlight masking by these units pass through the first array lens 3. Whenlight-masking unit 501 is arranged downstream of the first array lens 3(as viewed from the light source 1), light beams exiting from the firstarray lens 3 are subject to light masking. In FIG. 7, optical elementsafter the superimposing lens 6 are omitted.

With a first embodiment, the light-masking unit is configured such thatthe light masks 502 and 503 are arranged outside the light beams, asshown in FIG. 8A, to maximize the amount of emitted light and that theunits are turned in the directions indicated by arrows 601 and 602 tomask light beams 700 when adjusting the amount of light masking.However, the light-masking unit may be configured such that the lightmasks 502 and 503 are arranged outside the light beams, as shown in FIG.8B, to maximize the amount of emitted light and that the units are movedin the direction indicated by arrows 603 and 604 to increase the amountof light masking.

Furthermore, the light-masking unit may be configured such that they arearranged in parallel with the optical axis in light beams, as shown inFIG. 8C, to maximize the amount of emitted light and that the units areturned in the direction indicated by arrows 605 and 606 to increase theamount of light masking.

A second embodiment is explained below. The second embodiment is amodified version of the first embodiment, wherein the light-maskingmethod based on light masks has been changed. FIG. 9 shows, from thelight source side, a condition that light masks 506 and 507 areprojected on the first array lens 3. A hatched section 508 is alight-masking section formed by projecting the light mask 506; a hatchedsection 509 is a light-masking section formed by projecting the lightmask 507.

FIG. 9A shows a condition that the amount of light emitted from thelight source is maximized; FIG. 9B shows a condition that the amount oflight emitted from the light source is minimized. When the amount ofemitted light is adjusted as shown in FIG. 9B with this embodiment, thecells included in the sections 422, having the highest rate ofcontribution to the illumination intensity, are all light-masked. Then,sections 555 include cells without entire masking of light beams i.e.,cells with partial transmission of light beams from the light source,having the highest rate of contribution to the illumination intensity.The amount of light masking can be increased while maintaining moreuniform illumination distribution superimposed on the image displayelement by making the area of the light-masking section at cellsincluded in the sections 555 smaller than the area of the light-maskingsection at other cells.

With the amount of light emitted from the light source adjusted to theminimized level with the embodiment in FIG. 9, the amount of lightmasking can be increased while maintaining more uniform illuminationdistribution superimposed on the image display element by making thearea of the light-masking section at cells in the center section 421,having a low rate of contribution of the illumination intensity, largerthan the area of the light-masking section at the cells included in thesections 555.

It is desirable that the area of the light-masking section at cells inthe sections 555, among cells without entire masking of light beams, benot more than one half of the area of the cells as shown in FIG. 9B. Thereason is explained above with reference to FIG. 1.

With the embodiments in FIG. 5 and FIG. 9, it is possible to maintainmore uniform illumination distribution superimposed on the image displayelement while increasing the amount of light masking. Therefore, bymaking the amount of emitted light not more than 20% of the maximumamount of light emitted from the light source when adjusting the amountof light emitted from the light source from the maximum level to theminimum level, the uniformity level of the illumination distribution canbe made practically problem-free even if all cells except 2 to about 16cells, for example, are light-masked with the amount of light adjustedto the minimum level.

Since it is possible to maintain more uniform illumination distributionsuperimposed on the image display element while increasing the amount oflight masking, even if all the array lens cells are partially orentirely light-masked, i.e., cells are at least partly light-masked,with the amount of light emitted from the light source adjusted to theminimum level as shown in the embodiments in FIG. 5 and FIG. 9B, theuniformity level of the illumination distribution can be madepractically problem-free.

With these embodiments, furthermore, the first array lens 3 isconfigured such that rectangular cells are arranged, in line symmetry tothe two axes which pass through and perpendicularly intersect theoptical axis, in even-number columns. When rectangular cells arearranged in parallel with two arbitrary axes perpendicularlyintersecting a general optical axis, there are three differentarrangements of array lens cells as shown in FIG. 10A, FIG. 10B and FIG.10C. FIG. 10A shows the array lens configuration used in the embodimentsin FIG. 5 and FIG. 9. Cells included in the sections 422, having thehighest rate of contribution to the illumination intensity explained inthese embodiments, may be cell sections 552 shown in FIG. 10A. However,this configuration has the same meaning as the sections 422 because itcan be made simply by rotating the sections 422 by 90 degrees centeringaround the optical axis.

With a third embodiment, the configuration of the first array lens 3 inFIG. 10A has been modified to the array lens configuration shown in FIG.10B. Specifically, the array lens is configured such that rectangularcells are arranged, in line symmetry to the two axes which pass throughand perpendicularly intersect the optical axis, in even-number columnsin terms of one axis and odd-number columns in terms of the other axis.A cell section 421 including the center cells on the array lens in FIG.10A corresponds to a cell section 545 on the array lens in FIG. 10B.Cell sections 552 on the array lens in FIG. 10A correspond to cellsections 563 or cell sections 567 on the array lens in FIG. 10B. Othercell sections are the same as those in the embodiments in FIG. 5 andFIG. 9. Even if arrangements of even-number columns and odd-numbercolumns are reversed, the same configuration can be made simply byrotating the array lens arrangement shown in FIG. 10B by 90 degrees.

With a forth embodiment, the configuration of the first array lens 3 inFIG. 10A has been modified to the array lens configuration shown in FIG.10C. Specifically, the array lens is configured such that rectangularcells are arranged, in line symmetry to the two axes which pass throughand perpendicularly intersect the optical axis, in odd-number columns interms of one axis and odd-number columns in terms of the other axis. Acell section 421 including the center cells on the first array lens 3 inFIG. 10A corresponds to the center cell 546 on the array lens in FIG.10C. Cell sections 422 on the first array lens 3 in FIG. 10A correspondto cell sections 569 or cell sections 571 on the array lens in FIG. 10C.

In either example in FIG. 10, cells contacting the optical axispenetrating through the first array lens 3 (four cells in the section421 in FIG. 10A, two cells in the section 545 in FIG. 10B, and one cellin the section 546 in FIG. 10C) and cells sharing a side are recognizedas cells having the highest rate of contribution to the illuminationintensity. The area of the light-transmitting section at these cells ismade larger than the area of the light-transmitting section at othercells.

According to the above-mentioned embodiments, as mentioned above, aprojection type image display apparatus using a light-masking unit basedon light masks makes it possible to obtain images with a wide dynamicrange while maintaining more uniform illumination distribution.

A calculating section (not shown) calculates the amount of light to bemasked from an input image signal and then converts it into a signal fordriving a driving apparatus (not shown) such as a motor. The amount oflight masking is converted into the amount of movement and amount ofturn of the light masks and then adjusted through driving by theabove-mentioned driving apparatus.

What is claimed is:
 1. A projection type image display apparatus,comprising; a light source which emits light; an optical system whichincludes a first array lens and a second array lens; optical elementswhich separate light from the optical system into 3 different lights ofdifferent color bands, light valves, the respective light valves receivethe respective 3 different lights; a projection lens which projectslights from the light valves; and a light-masking unit which has onlytwo light-masking plates to be turned or moved so as to adjust a lightmasking amount by masking light beams between the first array lens andthe second array lens, each of the two light-masking plates includes aflat surface to mask the light beams, light beams that are not masked bythe light-masking unit are going to be separated by the opticalelements, wherein, the first array lens has a plurality of lens cellsarranged in a first direction and a second direction, an arrangement ofthe plurality of lens cells in the first array lens is line symmetry toboth the first direction and the second direction, including: 1) atleast one center lens cell arranged most close to a center of thearrangement of the plurality of lens cells in the first array lens, 2)at least one first adjacent lens cell adjacent to the at least onecenter lens cell in the first direction away from the center of thearrangement of the plurality of lens cells in the first array lens, and3) at least one second adjacent lens cell adjacent to the at least onecenter lens cell in the second direction away from the center of thearrangement of the plurality of lens cells in the first array lens, inone light-masking condition, the light-masking unit masks light beamsbetween the first array lens and the second array lens so that not lessthan 80% of the amount of light which is emitted from the light sourceand reaches the light valve is masked by the two light-masking plates;both the at least one center lens cell and the at least one firstadjacent lens cell are partially light-masked and partially open; and alight masking ratio of the at least one center lens cell is differentfrom a light masking ratio of the at least one first adjacent lens cell.2. The projection type image display apparatus as defined in claim 1,wherein each of one lens cell or more lens cells arranged in the seconddirection next to the at least one second adjacent lens cell is entirelylight-masked in said light-masking condition.
 3. The projection typeimage display apparatus as defined in claim 1, wherein the light-maskingunit turns or moves the two light-masking plates to adjust a lightmasking amount in the direction parallel to the second direction.
 4. Theprojection type image display apparatus as defined in claim 1, whereinthe amount of light masked by the light-masking unit increases when thetwo light-masking plates are turned or moved close to each other by thelight-masking unit.
 5. The projection type image display apparatus asdefined in claim 1, wherein each of the two light-masking plates has apartially straight-line edge.
 6. The projection type image displayapparatus as defined in claim 1, wherein the optical system includes asuperimposing lens.
 7. The projection type image display apparatus asdefined in claim 1, wherein in said light-masking condition, alight-masking area for the at least one first adjacent lens cell issmaller than a light-masking area for the at least one center lens cell.8. A projection type image display apparatus, comprising; a light sourcewhich emits light; an optical system which includes a first array lensand a second array lens; optical elements which separate light from theoptical system into 3 different lights of different color bands, lightvalves, the respective light valves receive the respective 3 differentlights; a projection lens which projects lights from the light valves;and a light-masking unit which has only two light-masking plates to beturned or moved so as to adjust a light masking amount by masking lightbeams between the first array lens and the second array lens, whereineach of the two light-masking plates includes a flat surface to mask thelight beams, light beams that are not masked by the light-masking unitare going to be separated by the optical elements, wherein, the firstarray lens has a plurality of lens cells arranged in a first directionand a second direction, an arrangement of the plurality of lens cells inthe first array lens is a line symmetry to both the first direction andthe second direction, including: 1) at least one center lens cellarranged most close to a center of the arrangement of the plurality oflens cells in the first array lens, 2) at least one first adjacent lenscell adjacent to the at least one center lens cell in the firstdirection away from the center of the arrangement of the plurality oflens cells in the first array lens, and 3) at least one second adjacentlens cell adjacent to the at least one center lens cell in the seconddirection away from the center of the arrangement of the plurality oflens cells in the first array lens, in one light-masking condition, thelight-masking unit masks light beams between the first array lens andthe second array lens so that not less than 80% of the amount of lightwhich is emitted from the light source and reaches the light valve ismasked by the two light-masking plates; both the at least one centerlens cell and the at least one first adjacent lens cell are partiallylight-masked and partially open; and a shape of a light masking area forthe at least one center lens cell is different from a shape of a lightmasking area for the at least one first adjacent lens cell.
 9. Theprojection type image display apparatus as defined in claim 8, whereineach of one lens cell or more lens cells arranged in the seconddirection next to the at least one second adjacent lens cell is entirelylight-masked in said light-masking condition.
 10. The projection typeimage display apparatus as defined in claim 8, wherein the light-maskingunit turns or moves the two light-masking plates to adjust a lightmasking amount in the direction parallel to the second direction. 11.The projection type image display apparatus as defined in claim 8,wherein the amount of light masked by the light-masking unit increaseswhen the two light-masking plates are turned or moved close to eachother by the light-masking unit.
 12. The projection type image displayapparatus as defined in claim 8, wherein each of the two light-maskingplates has a partially straight-line edge.
 13. The projection type imagedisplay apparatus as defined in claim 8, wherein the optical systemincludes a superimposing lens.
 14. The projection type image displayapparatus as defined in claim 8, wherein in said light-maskingcondition, a light-masking area for the at least one first adjacent lenscell is smaller than a light-masking area for the at least one centerlens cell.
 15. A projection type image display apparatus, comprising; alight source which emits light; an optical system which includes a firstarray lens and a second array lens; optical elements which separatelight from the optical system into 3 different lights of different colorbands, light valves, the respective light valves receive the respective3 different lights; a projection lens which projects lights from thelight valves; and a light-masking unit which has only two light-maskingplates to be turned or moved so as to adjust a light masking amount bymasking light beams between the first array lens and the second arraylens, each of the two light-masking plates includes a flat surface tomask the light beams, light beams that are not masked by thelight-masking unit are going to be separated by the optical elements,wherein, the first array lens has a plurality of lens cells arranged ina first direction and a second direction, an arrangement of theplurality of lens cells in the first array lens is line symmetry to boththe first direction and the second direction, including: 1) at least onecenter lens cell arranged most close to a center of the arrangement ofthe plurality of lens cells in the first array lens, 2) at least onefirst adjacent lens cell adjacent to the at least one center lens cellin the first direction away from the center of the arrangement of theplurality of lens cells in the first array lens, and 3) at least onesecond adjacent lens cell adjacent to the at least one center lens cellin the second direction away from the center of the arrangement of theplurality of lens cells in the first array lens, in one light-maskingcondition, the light-masking unit masks light beams between the firstarray lens and the second array lens so that not less than 80% of theamount of light which is emitted from the light source and reaches thelight valve is masked by the two light-masking plates; both the at leastone center lens cell and the at least one first adjacent lens cell arepartially light-masked and partially open; and a light masking ratio ofthe at least one center lens cell is different from a light maskingratio of the at least one first adjacent lens cell, and wherein, in theone light-masking condition, a shape of light masking area for the totalof the plurality of the lens cells is line symmetry to both the firstdirection and the second direction.
 16. The projection type imagedisplay apparatus as defined in claim 15, wherein each of one lens cellor more lens cells arranged in the second direction next to the at leastone second adjacent lens cell is entirely light-masked in saidlight-masking condition.
 17. The projection type image display apparatusas defined in claim 15, wherein the light-masking unit turns or movesthe two light-masking plates to adjust a light masking amount in thedirection parallel to the second direction.
 18. The projection typeimage display apparatus as defined in claim 15, wherein the amount oflight masked by the light-masking unit increases when the twolight-masking plates are turned or moved close to each other by thelight-masking unit.
 19. The projection type image display apparatus asdefined in claim 15, wherein each of the two light-masking plates has apartially straight-line edge.
 20. The projection type image displayapparatus as defined in claim 15, wherein the optical system includes asuperimposing lens.
 21. The projection type image display apparatus asdefined in claim 15, wherein in said light-masking condition, alight-masking area for the at least one first adjacent lens cell issmaller than a light-masking area for the at least one center lens cell.22. A projection type image display apparatus, comprising; a lightsource which emits light; an optical system which includes a first arraylens and a second array lens; optical elements which separate light fromthe optical system into 3 different lights of different color bands,light valves, the respective light valves receive the respective 3different lights; a projection lens which projects lights from the lightvalves; and a light-masking unit which has only two light-masking platesto be turned or moved so as to adjust a light masking amount by maskinglight beams between the first array lens and the second array lens,wherein each of the two light-masking plates includes a flat surface tomask the light beams, light beams that are not masked by thelight-masking unit are going to be separated by the optical elements,wherein, the first array lens has a plurality of lens cells arranged ina first direction and a second direction, an arrangement of theplurality of lens cells in the first array lens is line symmetry to boththe first direction and the second direction including: 1) at least onecenter lens cell arranged most close to a center of the arrangement ofthe plurality of lens cells in the first array lens, 2) at least onefirst adjacent lens cell adjacent to the at least one center lens cellin the first direction away from the center of the arrangement of theplurality of lens cells in the first array lens, and 3) at least onesecond adjacent lens cell adjacent to the at least one center lens cellin the second direction away from the center of the arrangement of theplurality of lens cells in the first array lens, in one light-maskingcondition, the light-masking unit masks light beams between the firstarray lens and the second array lens so that not less than 80% of theamount of light which is emitted from the light source and reaches thelight valve is masked by the two light-masking plates; both the at leastone center lens cell and the at least one first adjacent lens cell arepartially light-masked and partially open; and a shape of a lightmasking area for the at least one center lens cell is different from ashape of a light masking area for the at least one first adjacent lenscell, and wherein, in the one light-masking condition, a shape of lightmasking area for the total of the plurality of the lens cells is linesymmetry to both the first direction and the second direction.
 23. Theprojection type image display apparatus as defined in claim 22, whereineach of one lens cell or more lens cells arranged in the seconddirection next to the at least one second adjacent lens cell is entirelylight-masked in said light-masking condition.
 24. The projection typeimage display apparatus as defined in claim 22, wherein thelight-masking unit turns or moves the two light-masking plates to adjusta light masking amount in the direction parallel to the seconddirection.
 25. The projection type image display apparatus as defined inclaim 22, wherein the amount of light masked by the light-masking unitincreases when the two light-masking plates are turned or moved close toeach other by the light-masking unit.
 26. The projection type imagedisplay apparatus as defined in claim 22, wherein each of the twolight-masking plates has a partially straight-line edge.
 27. Theprojection type image display apparatus as defined in claim 22, whereinthe optical system includes a superimposing lens.
 28. The projectiontype image display apparatus as defined in claim 22, wherein in saidlight-masking condition, a light-masking area for the at least one firstadjacent lens cell is smaller than a light-masking area for the at leastone center lens cell.